In the aforementioned three-dimensional shaping method, it is currently impossible to completely prevent sintering defects, due to the following reasons:
A. A problem with the laser beam or electron beam control system may result in an excess or insufficiency of the supplied beam, forming a non-flat sintering surface with a generally regular uneven condition, compared to when each beam is supplied normally,
B. Due to formation of the uneven condition of above A or infiltration of chips during formation of the powder layer supplied by the powder supply apparatus, squeegee movement is hampered and it becomes difficult to achieve a uniform flat surface, or melting with the previously sintered layer may be incomplete, causing abnormalities in the powder layer surface that result in a non-flat powder layer surface with an irregular uneven condition.
However, since in a three-dimensional shaping method, the laminating and sintering steps are repeated in a sealed apparatus, it is unavoidable that such sintering defects as mentioned in above A and B will be overlooked and only noticed after completion of all of the laminating steps and all of the sintering steps that have been repeated.
Detection of deterioration or defects generated in structures by irradiation and scattering of light is already publicly known, as disclosed in Patent Documents 1, 2 and 3, for example.
In addition, detection of the positions of cracks in structures such as ceramic bodies by the scattering of light is also publicly known, as disclosed in Patent Documents 4 and 5, for example.
However, the prior arts neither disclose nor suggest the appropriate use of technology relating to light reflection for three-dimensional shaping methods.